Exhaust aftertreatment systems are used to chemically convert or physically remove constituents from a combustion engine exhaust stream. Operation of such exhaust aftertreatment systems may benefit from the ability to inject a fluid into the exhaust stream. For example, some catalytic converters used for selective catalytic reduction (SCR) require injection of reductant into combustion exhaust upstream of the catalyst to effect the desired chemical species conversion. Similarly, regeneration of a diesel particulate filter (DPF) may benefit from upstream injection of a combustible fluid into the exhaust stream. In these cases, a fluid injector would be located upstream of each device.
The fluid injector may include a valve located between a pressurized fluid supply and an injector nozzle, where the injector nozzle is exposed to the exhaust stream. In such an injector, minimizing the distance from the injector valve to the injector nozzle tip may be advantageous with respect to injection spray characteristics and mechanical packaging considerations, but can result in detrimental overheating of the injector valve. Further, overheating of residual fluid within the injector can cause detrimental corrosion or boiling within the injector.
Flow of the fluid through the injector can transfer heat away from the injector. However, some system operating modes may require the injector valve to close for significant time durations, thereby stopping the flow of the fluid through the injector. Accordingly, cooling the injector with the fluid may not be sufficient across all operating modes for an exhaust aftertreatment system.
U.S. Pat. No. 7,877,990 discloses a metering device cooling system including a cooling circuit having a cooling device that transfers heat out of the cooling circuit, where at least a part of the cooling circuit is disposed below the cooling device and at least another part of the cooling circuit is disposed above a point where heat is added to the cooling circuit. However, the need for a cooling device adds undesirable complexity, and may require vehicle motion to drive sufficient heat transfer.
Accordingly, improved apparatus and methods for cooling injectors that are mounted on a combustion engine exhaust duct are desired.